Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO 3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0?≤?x?≤ 1·0) with a step-wise increment of 0·10 in the glass [(Pb _x Sr_1???x )OTiO₂]–[(2SiO₂B₂O₃)]–[BaO·K₂O]·Nb₂O₅ (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm^???1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (~27 °C) to 1400 °C employing a heating rate of 10 °C /min to determine glass transition temperature, T _g and crystallization temperature, T _c. The melting temperature, T _m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. T _g and T _m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with x ≤ 0·5 was found to have cubic structure similar to SrTiO₃ ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.     

Design and preparation of high-performance amine-based poly(ether ketone)s with strong photonic luminescence

Amine-based poly(ether ketone)s (A-PEKs), as novel high-performance functional polymers, have been obtained by the polycondensation of dibromo ketones with aromatic ether diamines via palladium-catalyzed aryl amination reaction. The structures of the polymers are characterized by means of FT-IR, ¹H NMR spectroscopy and elemental analysis, the results show a good agreement with the proposed structures. DSC and TGA measurements exhibit that polymers possess high glass transition temperature (T _g ≥ 175 °C) and good thermal stability with high decomposition temperatures (T ₅ ≥ 400 °C). Based on the hydrogen bonds between the polymer chains, thin films of A-PEKs show great mechanical behaviors with high tensile strength up to 89.5 Mpa. In addition, due to the photoinduced intramolecular charge-transfer (ICT) of A-PEKs, these synthesized polymers are endowed with significantly strong photonic luminescence in N,N′-dimethylformamide.     

An approach to prepare defect-free PES/MFI-type zeolite mixed matrix membranes for CO2/N2 separation

Polyethersulfone (PES) and MFI-type zeolite mixed matrix membranes (MMMs) were successfully fabricated by a novel particle suspension impregnating and solution-casting method. The effects of two different membrane preparation methods on the membrane morphology were investigated by scanning electron microscopy; the particle crystal type and distribution were explored by X-ray diffraction and fourier transform attenuated total reflectance infrared spectroscopy. The results showed that the MFI-zeolite particles were successfully synthesized, with particle diameter around 250 nm. Distribution and dispersion of MFI-zeolite particles suspended in the polymer matrix are homogeneous and uniform. The thermal analysis indicates that the glass transition temperature (T _g) of MMMs is around 230 °C and the initial degradation temperature is up to 460 °C in air. The increment of T _g compared to the neat PES confirms that the polymer chain rigidification is induced by zeolite particles. The MMMs have been evaluated by the CO₂/N₂ separation factor and permeability measured as a function of permeation temperature, the maximum separation factor of the PES/10 % MFI-silica zeolite for the pure gas reaches 35 at 25 °C.     

Compressive Strength of Notched Poly(Phenylene Sulfide) Aerospace Composite: Influence of Fatigue and Environment

The purpose of this work is to evaluate the influences of fatigue and environmental conditions (?55 °C, 23 °C, and 82 °C/Wet) on the ultimate compression strength of notched carbon-fiber-reinforced poly(phenylene sulfide) composites by performing open-hole compression (OHC) tests. Analysis of the fatigue effect showed that at temperatures of ?55 and 23 °C, the ultimate OHC strengths were higher for fatigued than for not-fatigued specimens; this could be attributed to fiber splitting and delamination during fatigue cycling, which reduces the stress concentration at the hole edge, thus increasing the composite strength. This effect of increasing strength for fatigued specimens was not observed under the 82 °C/Wet conditions, since the test temperature near the matrix glass transition temperature (T _g) together with moisture content resulted in matrix softening, suggesting a reduction in fiber splitting during cycling; similar OHC strengths were verified for fatigued and not-fatigued specimens tested at 82 °C/Wet. Analysis of the temperature effect showed that the ultimate OHC strengths decreased with increasing temperature. A high temperature together with moisture content (82 °C/Wet condition) reduced the composite compressive strengths, since a temperature close to the matrix T _g resulted in matrix softening, which reduced the lateral support provided by the resin to the 0° fibers, leading to fiber instability failure at reduced applied loads. On the other hand, a low temperature (?55 °C) improved the compressive strength because of possible fiber-matrix interfacial strengthening, increasing the fiber contribution to compressive strength.     

Growth and characterization of III-N bulk crystals

Hexagonal BN crystals were grown from solution by application of a thermal gradient. The solvent used to dissolve the source was optimized by changing the ratio of components to have the lowest melting point. The investigation of adding a third component demonstrated further reduction of the melting point with BN as an additive. A solution was created with enhanced properties allowing the growth of BN. BN was grown on a PBN seed at T _g = 900 °C and P = 0.2 MPa for approximately 65 h. The BN crystals were found to be embedded in a solvent matrix, as determined by EDS. In addition, GaN crystals were grown in a modified solution at T _g = 800 °C and P = 0.2 MPa. Raman spectroscopy verified wurtzite GaN structure with good crystallinity. The successful growth of BN and GaN from solution suggests this to be a method of choice for growth of the III-Ns, and may prove to be a viable alternative to current costly wafer production techniques.     

Effect of the adding of rod-like attapulgite upon the properties of polyimides produced by random copolycondensation

A series of polyimides (PIs) and polyimide/attapulgite (AT) composite films was successfully prepared by random copolycondensation. The polyimides were synthesized based on 4,4′-diaminodiphenyl ether, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), and 4,4′-oxydiphthalic anhydride (ODPA). By adjusting the ratio of BPADA and ODPA, three different types of anhydride group-terminated PIs were obtained. AT was functionalized by chemical modification with γ-aminopropyltriethoxysilane and then chemical bonded with PI via reaction between amino group and anhydride group, resulting in stable PI/AT composites. The structure and properties of PIs and PI/AT composites were characterized by FTIR, XRD, TG, SEM, DSC, DMA, mechanical measure, and so on. Comparison was given between PIs and PI/AT composites. Results showed that all PIs had good thermal stability and mechanical properties with glass translation temperature (T _g) over 210 °C, 5 % weight loss temperature (T _d,5%) over 494 °C and tension strength of 84–89.9 MPa, breaking elongation around 7 %. More stable, flexible, and much stronger films were obtained after adding 5 wt% AT, which showed 535–548.5 °C, 85.8–118.9 MPa, and 10.3–24.7 % in T _d,5%, tension strength, and breaking elongation, respectively. Much interestingly, we found that AT had the greatest effect on PI-2, the yielding of which occurred during mechanical measure, and PI/AT-2 composite displayed excellent comprehensive properties.     

Fabrication and characterization of thermo-responsive GO nanosheets with controllable grafting of poly(hexadecyl acrylate) chains

A series of novel poly(hexadecyl acrylate)-grafted-graphene oxides (PHDA-g-GOs) were fabricated as thermo-responsive GO nanosheets via diazonium addition and surface-initiated atom transfer radical polymerization (SI-ATRP). Various spectroscopic and microscopic evidences confirm the successful fabrication of the thermo-responsive GO nanosheets. The thermo-responsive property and thermal stability of the PHDA-g-GOs were determined by DSC and TGA. Furthermore, we have demonstrated the ability to systematically tune the chain length of polymer molecules covalently bonded to GO nanosheets by SI-ATRP. Comparing the thermo-responsive GO samples, the ?H _m and ?H _c increased as the molar ratio of monomer to initiator increased. Moreover, the T _mo, T _co, ?H _m and ?H _c values of the PHDA-g-GO3 (with a molar ratio of monomer to initiator as 1000:1) are 31.2, 31.4 °C, 79 and 76 J/g, respectively. Meanwhile, the thermo-responsive GO nanosheets have good thermal stability and shape stability. Therefore, the thermo-responsive GO nanosheet is a very promising functional material and can be used in more areas, such as the fabrication of temperature-sensitive drugs, reagents, fibers and textiles, solar energy storage and temperature sensor.     

Glass transitions of hygrothermal aged pultruded glass fibre reinforced polymer rebar by dynamic mechanical thermal analysis

The changes that can occur in glass fibre reinforced polymer (GFRP) composites with ageing can affect its application, performance and lifetime. Hygrothermal ageing (i.e. accelerated ageing by moisture absorption and temperature change) is a very useful technique to evaluate durability as well as development of GFRP composites in a reasonable timeframe. Dynamic mechanical thermal analysis (DMTA) is essentially able to detect all changes in the state of molecular motion in polymer composites as temperature is scanned. In this work, pultruded GFRP rebars were accelerated aged in an alkaline aqueous environment at 60 °C for 1, 2, 3, 4 and 6 months to evaluate the changes in glass transition of viscoelastic GFRP rebars by DMTA. Five different glass transitions in an average temperate range from 110 to 165 °C were observed at storage modulus, loss modulus and damping factor traces of DMTA. It was also found that glass transition temperature (T_g) of the aged samples changed up to maximum 6 °C compared with that of controlled sample. This change in T_g with ageing time was believed to be due to moisture absorption by rebars.     

Formation and properties of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

A new glass system SnO–MgO–P₂O₅ with low viscosity has been developed by a melt-quenching method. Formation, thermal properties, and chemical durability of these glasses have been investigated. For a constant P₂O₅ concentration, the glass formation ability is enhanced with the increasing Sn/(Sn + Mg) ratio. The glasses exhibit low glass transition temperature (T _g = 270–400 °C), low dilatometric softening temperature (T _DS = 290–420 °C), and high thermal expansion coefficient (CTE = 110–160 × 10⁻⁷ K⁻¹). With the increasing Sn/(Sn + Mg) ratio, T _g and T _DS decrease, and CTE increases. When Sn/(Sn + Mg) ratio is varied, the relationship between chemical durability and thermal properties of the present glasses is not consistent with what expected in general cases. It is noted that the glasses with 32–32.5 mol% P₂O₅ exhibit excellent chemical durability and tunable T _g, T _DS, and CTE (by varying Sn/(Sn + Mg) ratio).     

Thermal stability and fire behavior of aluminum diethylphosphinate-epoxy resin nanocomposites

The flame retardancy of 2, 2-bis(4-glycidyloxyphenyl)propane (DGEBA)-aluminum diethylphosphinate (AlPi) nanocomposites (EP-AlPi/(P ? x), x = 1, 2, 3 %) was greatly enhanced by ultrasonic dispersion of nano-sized AlPi into epoxy resin. The UL 94 V-0 rating can be reached for EP-AlPi nanocomposites with a relatively low addition amount of AlPi (on the account of 8.4 wt% or phosphorus content of 2 wt%) as well as the LOI value over 37.2. The glass transition temperature (T _g) enhanced properties were investigated by DTA, which showed that: T _gs were about 5 °C higher than that of neat epoxy resin; T _g increased along with content increasing of AlPi. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of EP-AlPi/(P ? x) composites were studied by Kissinger’s, Ozawa’s, Flynn–Wall–Ozawa’s and Coast-Redfern’s methods, which suggested the conversion function f (α) = 1/2α ^?1 or f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 1 %); f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 2 %) and EP-AlPi/(P ? 3 %) during the investigated process. The epoxy resin nanocomposites obtained in this study are green functional polymers and will become flame retardant potential candidates in electronic fields such as printed wiring boards with high performance.     

Effect of annealing on the thermal expansion and residual stresses of bidirectional thermoplastic composite laminates

Thermal expansion measurements have been conducted on various [(±30)_N]_S laminates fabricated by combining different types of matrix and fibers. The main objective was to link the coefficient of thermal expansion (CTE) of these laminates to the thermophysical characteristics of the matrix. The results show how these laminates can be used to analyze the influence of annealing and glass transition temperatures on the CTE and the release of residual stresses. It is shown that to ensure a reproductive expansion during thermal cycling, the composite must be annealed at a temperature high enough over T_g of the matrix (below the melt temperature) in order to completely release the residual stresses induced during the molding phase and uniformize the crystalline structure of the matrix. Once this is done, the response of the material under thermal cycling gives reproducible coefficient of thermal expansion (CTE) with almost no distortion after each cycle.     

The effect of ZrO2 and TiO2 on solubility and strength of apatite–mullite glass–ceramics for dental applications

The effect of ZrO₂ and TiO₂ on the chemical and mechanical properties of apatite–mullite glass–ceramics was investigated after sample preparation according to the ISO (2768:2008) recommendations for dental ceramics. All materials were characterized using differential thermal analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray fluorescence spectroscopy was used to determine the concentrations of elements present in all materials produced. The chemical solubility test and the biaxial flexural strength (BFS) test were then carried out on all the samples. The best solubility value of 242 ± 61 μg/cm² was obtained when HG1T was heat-treated for 1 h at the glass transition temperature plus 20 °C (T_g + 20 °C) followed by 5 h at 1200 °C. The highest BFS value of 174 ± 38 MPa was achieved when HG1Z and HG1Z+T were heat-treated for 1 h at the T_g + 20 °C followed by 7 h at 1200 °C. The present study has demonstrated that the addition of TiO₂ to the reference composition showed promise in both the glass and heat-treated samples. However, ZrO₂ is an effective agent for developing the solubility or the mechanical properties of an apatite–mullite glass–ceramic separately but does not improve the solubility and the BFS simultaneously.     

Synthesis, characterization, and biological activities of organosoluble and thermally stable xanthone-based polyamides

A series of polyamides, poly (xanthone-amide)s (PXAs) were prepared by direct polycondensation of 2,7-diaminoxanthone with various available aliphatic and aromatic dicarboxylic acids. The monomer and all the PXAs were characterized by FT-IR, ¹H NMR and ¹³C NMR. The prepared polyamides showed inherent viscosities in the range of 0.41–0.68 dL g^?1 in NMP at 25 °C. The PXAs with low crystallinity were soluble in aprotic polar solvents such as DMF, NMP, DMSO, and DMAc at room temperature. These PXAs showed low glass transition temperatures (T _g) (200–310 °C) and high thermal stability, the 10 % weight loss temperature was up to 432 °C under nitrogen. These polymers exhibited strong UV–Vis absorption maxima at 301–316 nm in NMP solutions. Their photoluminescence showed fluorescence emission maxima around 433–444 and 503–521 nm for aliphatic and aromatic polyamides, respectively. The resulting polymers were analyzed for their antioxidant activities using DPPH assay and the antibacterial activities against some bacterial strains (S. aureus, B. subtilis, E. coli and P. aeruginosa). The results revealed that the antioxidant and antibacterial activities of PXAs were more than xanthone nucleus and used standard, respectively. It showed that these polymers can be used in pharmaceutical and food industries (food packaging).     

The Potential of Small-Scale Fusion Experiments and the Gordon-Taylor Equation to Predict the Suitability of Drug/Polymer Blends for Melt Extrusion

The aim of this study was to investigate the use of small-scale fusion experiments and the Gordon-Taylor (GT) equation to predict whether melt extrusion of a drug with an amorphous polymer produces a stable amorphous dispersion with increased drug dissolution. Indomethacin, lacidipine, nifedipine, piroxicam, and tolbutamide were used as poorly soluble drugs. Drug/polyvinylpyrrolidone (PVP) blends were prepared at a 1:1 mass ratio. Small-scale fusion experiments were performed in a differential scanning calorimeter (DSC) and in stainless steel beakers. Extrusion was performed in a Brabender Plasti-corder. The glass transition temperatures T_g were determined by DSC. Taking an average T_g from the DSC melt, beaker melt, and GT equation accurately predicted the extrudate T_g. Physical stability of beaker melt and extrudate samples was tested by X-ray powder diffraction (XRPD) and DSC after storage at 30°C (beaker melt) or 25°C (extrudate) and less than 10%, 60%, and 75% relative humidity (RH). Beaker melts were amorphous, apart from some residual crystallinity. Extrudates were amorphous after preparation. Except for indomethacin/PVP, which remained amorphous, the crystallinity of beaker melts and extrudates increased only at 75% RH. Recrystallization occurred even when the T_g of the sample was well above the storage temperature. Chemical stability of the beaker melts and extrudates was tested by capillary electrophoresis and high-performance liquid chromatography (HPLC). Stability was slightly improved in the extrudate compared to the beaker melt. In general, the order for rate of dissolution was crystalline drug was less than the physical mixture, which was less than the drug/PVP beaker melt, which was approximately equal to the extrudate. The use of beaker melts allows a conservative estimate of the potential to melt extrude a drug. To predict physical stability, analysis of the T_g must be combined with physical stability experiments.     

Interface modification of clay and graphene platelets reinforced epoxy nanocomposites: a comparative study

The interface between the matrix phase and dispersed phase of a composite plays a critical role in influencing its properties. However, the intricate mechanisms of interface are not fully understood, and polymer nanocomposites are no exception. This study compares the fabrication, morphology, and mechanical and thermal properties of epoxy nanocomposites tuned by clay layers (denoted as m-clay) and graphene platelets (denoted as m-GP). It was found that a chemical modification, layer expansion and dispersion of filler within the epoxy matrix resulted in an improved interface between the filler material and epoxy matrix. This was confirmed by Fourier transform infrared spectroscopy and transmission electron microscope. The enhanced interface led to improved mechanical properties (i.e. stiffness modulus, fracture toughness) and higher glass transition temperatures (T _g) compared with neat epoxy. At 4 wt% m-GP, the critical strain energy release rate G _1c of neat epoxy improved by 240 % from 179.1 to 608.6 J/m² and T _g increased from 93.7 to 106.4 °C. In contrast to m-clay, which at 4 wt%, only improved the G _1c by 45 % and T _g by 7.1 %. The higher level of improvement offered by m-GP is attributed to the strong interaction of graphene sheets with epoxy because the covalent bonds between the carbon atoms of graphene sheets are much stronger than silicon-based clay.     

Novel nanocomposites based on epoxy resin/epoxy-functionalized polydimethylsiloxane reinforced with POSS

The purpose of the present study is to develop novel nanocomposites based on diglycidylether of bisphenol A (DGEBA) combined with diglycidylether-terminated polydimethylsiloxane (DG-PDMS), reinforced with 10 wt.% (mono-/octa) epoxy POSS nanocages (MEP or OEP-POSS). DG-PDMS and POSS compounds were covalently incorporated into DGEBA resin via copolymerization of epoxy groups. The effect of both DG-PDMS and POSS nanoparticles on the curing reaction, glass transition temperature (T_g), thermal stability, hardness and morphology of DGEBA/DG-PDMS ± POSS nanocomposites were studied by DSC, FTIR, DMA, TGA, SEM/EDX, AFM and contact angle measurements. SEM/EDX and AFM results prove that OEP-POSS is well dispersed within DGEBA/DG-PDMS polymer matrix, while MEP-POSS forms large POSS aggregates. The thermo-mechanical properties of POSS based nanocomposites are also in good correlation with morphology features. MEP-POSS based nanocomposite with heterogeneous dispersion of POSS aggregates exhibits lower T_g value and thermal stability in comparison with OEP-POSS nanocomposite which exhibits a nanoscale dispersion of the POSS cages. The obtained T_g of OEP-POSS based nanocomposite increases with 31 °C in comparison with the unreinforced matrix. Moreover, this nanocomposite shows the highest storage modulus (E′) and hardness.     

Synthesis and characterization of poly(silphenylenesiloxane)s containing functional side groups,a study to high-temperature elastomer

Poly(silphenylenesiloxane)s containing hydride or vinyl functional side groups were successfully synthesized by deaminative polycondensation of bis(aminosilane)s having the functional groups with monomeric or polymeric bis(silanol). The bis(silanol) prepolymer was prepared by palladium-catalyzed dehydrocoupling polymerization of 1,4-bis(dimethylsilyl)benzene with water. ¹H, ¹³C, and ²⁹Si NMR revealed that the polymers have exactly alternating structure of the starting component units. The poly(silphenylenesiloxane)s containing functional side groups have low T_gs ranging from −23 to −40 °C, and exhibit good thermal stability in both nitrogen and air atmosphere. For example, the most thermally stable polymer 3b-alt, having vinyl side groups on half silicon atoms, has T_g at –33°C which is 11°C lower than that of the all-methyl substituted PTMPS, and shows the highest degradation temperature at 498°C in nitrogen and 521°C in air. The TGA residues at 800°C are 67% in nitrogen and 54% in air. Isothermal studies revealed 3b-alt only lost 2.5% weight after 5h at 400°C in nitrogen.     

Effect of nanofiber on material properties of vapor-grown carbon nanofiber reinforced thermoplastic polyurethane (TPU/CNF) nanocomposites prepared by melt compounding

The present work deals with the preparation of the CNF based TPU nanocomposites by melt blending to explore the effect of state of dispersion and wt.% loading of CNF on material properties. In addition, the morphology, mechanical, thermal, rheological, and electrical properties of the nanocomposites have been evaluated through various characterization techniques with an aim to find the suitability of the nanocomposites for industrial applications. Transmission electron microscopy (TEM) study reveals that the CNFs exhibited a uniformly dispersed in TPU matrix. The thermal stability of the TPU evaluated by thermogravimetric analysis (TGA) showed significant increase with increased CNF content. It is observed that storage modulus (E′) and glass transition temperature (T_g) of the TPU matrix increases by the incorporation of CNF. The melting point (T_m) and the T_g of soft segments observed from the differential scanning calorimetry (DSC) were found to shift towards higher temperature with the inclusion of CNF.     

Colloidal particles with various glass transition temperatures: preparation, assembly, and the properties of stop bands under heat treatment

Monodisperse P(St-co-nBA-co-AA) colloidal microspheres with various glass transition temperatures (T _gs), whose average particle sizes were about 300 nm, were prepared using soap-free emulsion polymerization by adjusting the ratio of styrene and n-butyl acrylate. Colloidal photonic crystals were assembled with these microspheres by vertical deposition method. Stop bands of colloidal crystals under different temperatures have been characterized. The relationship between the stop band and temperature was indicated. The microstructure and reflectance spectra of photonic crystals were characterized by SEM and fiber spectrometer, respectively. Results showed that as the temperature increased, only a little red shift of stop band appeared in the vicinity of T _g and the intensity of the maximum reflection peak decreased until the stop bands disappeared. Furthermore, enough heating time at the T _g ±2 °C could also lead to the disappearance of stop bands. What’s more, colloidal crystal films with certain connection strength were obtained by simple heating.     

Accelerated thermal ageing of epoxy resin and 3-D carbon fiber/epoxy braided composites

This paper reports the accelerated thermal ageing behaviors of pure epoxy resin and 3-D carbon fiber/epoxy braided composites. Specimens have been aged in air at 90 °C, 110 °C, 120 °C, 130 °C and 180 °C. Microscopy observations and attenuated total reflectance Fourier transform infrared spectrometry analyses revealed that the epoxy resin oxidative degradation only occurred within the surface regions. The surface oxidized layer protects inner resin from further oxidation. Both the resin degradation and resin stiffening caused by post-curing effects will influence the compression behaviors. For the braided composite, the matrix ageing is the main ageing mode at temperatures lower than glass transition temperatures (T_g) of the pure epoxy resin, while the fiber/matrix interface debonding could be observed at the temperatures higher than T_g, such as the temperature of 180 °C. The combination of matrix degradation and fiber/resin interface cracking leads to the continuous reduction of compressive behaviors.